In June 2015, Police in Canterbury executed four search warrants as part of the investigation into the collapse of CTV building, saying any decision on charges would be made later that year.

They completed their investigation into the deaths last year and referred the file to Crown Law in June.

Detective Superintendent Peter Read said in December last year that the investigation was with the Crown Solicitor and would undergo a further legal review before the police made a final decision on charges.

At that time Mr Read was not able to say when the decision would be made, other than it would be in 2017.

A police spokesperson said the length of time being taken to determine a decision regarding prosecution reflected the complexity of the investigation.

The spokesperson said police were very mindful of the impact this was having on the victims' families and it was hoped there would be a decision soon.

The CTV building collapsed in the Christchurch earthquake on 22 February 2011, killing 115 people.

An Earthquakes Royal Commission found in 2012 that the building - designed by Dr Alan Reay's company - should not have been issued a building permit and the design was deficient in several ways.

It said the building was given a green sticker after the September 2010 earthquake, even though an engineer had not assessed it.

The Commission said the building sustained further damage in the Boxing Day 2010 earthquake, after which another level-one assessment was carried out, and the building was issued another green sticker.

The Institution of Professional Engineers (IPENZ) dropped its investigation into Mr Reay in 2014 after he resigned his membership.

That decision was appealed by the Attorney-General at the time, Chris Finlayson, who asked the courts to reconsider whether IPENZ should continue with its investigation.

In 2016, the Court of Appeal asked for both parties to refile their claims with a number of amendments before the matter is considered by the High Court.

The lead designer of the building, David Harding, was suspended from the register of Chartered Professional Engineers and ordered to pay $10,000 in 2014.